1. Field of the Invention
The present invention relates generally to a method and device for visual examination and self-examination of a person in natural everyday settings rather then in a setting of a medical laboratory. In particular, the method and device of the present invention allow for determination of a critical flicker fusion (CFF) frequency as an indicator of the person's physical and neurological condition. The device of the invention may be adapted to be used with a personal computer display or another commonly used monitor screen and as such can be projected over the existing viewing environment.
2. Description of the Prior Art
It is well established that various vision parameters can be used in assessing the general state of a human body. In the functioning of the body's nervous system, for example, data is transmitted between the sensory organs, brain and muscles via frequency-encoded nervous transmissions. Whenever a nerve fires, it must "rest" a while before firing again, which resting, or latency period varies depending on many factors, including physiological state. One way to measure the nerves' ability to conduct signals is to input a known signal varying in frequency over time at a sense organ, and test the brain's ability to detect the signal. A simple example is critical flicker fusion frequency (CFF) or flicker fusion frequency (FFF). A blinking light is typically presented to the eyes, and the blink frequency is increased until the light fuses or appears steady and unblinking. This critical fusion frequency is an indication of the physiological state of the nervous system. If CFF changes, nervous transmission speed may have been affected due to fatigue or other physiological or neurological change occurring at the synapses, thus affecting the ability of a person to properly gather and analyze sensory data. Normal CFF may be in the range between 50 Hz and 70 Hz, depending on several factors, including the portion of the retina which is stimulated. Viewing and lighting conditions during the test play the important role in the results of the CFF test as well.
It is well known that several diseases, i.e., multiple sclerosis, diabetes and glaucoma involve neurological deterioration. Such deterioration can be detected and the status of neurological function can be monitored by use of the CFF test. As a disease having neurological involvement with the optic pathways becomes more severe, the CFF for that person decreases. It is also known that the state of fatigue also reduces the CFF. In addition, the CFF varies due to some other factors such as the time of day, etc.
In the past, stationary or hand-held devices for detecting the critical flicker fusion frequency included mainly a stroboscope-type flickering target light, the frequency of which is adjustable. Typically, a person being tested observes the flickering target light with increasing frequency to the point at which it appears to be continuous, such frequency being that person's CFF frequency.
Prior to that method, a rotating drum with vertical stripes or other well distinguished objects was used for the same purpose. Increasing the speed of rotation would lead to the appearance of a single rotating body at a critical speed which once determined can be used to calculate the CFF. In fact, an argument can be made that this method of CFF determination is more physiologically accurate since a person would experience an object moving by much more frequently than a flashing light.
Examples of various devices for CFF testing can be found in the following U.S. Pat. Nos.: 4,324,460 by Daley; 3,891,311 by Fletcher; 3,814,510 by Adler; 3,737,217 by Haines; 3,424,519 by White, and a Statutory Invention Registration No. H293 by Task. All of these devices provide for CFF testing under defined conditions of viewing and lighting such as the distance from the screen, the brightness, color, and contrast of the flickering image (usually a large dot in the middle of the screen) as well as the level of surrounding light. Also, most of the devices require the person to go to the clinic or other medical office and be assisted by another person to perform the test.
At the same time, it is desirable to be able to perform the test at various times of the day and not to wait a long time before the next test appointment is available because the CFF value may change by then. Frequently, the person working with his computer feels the eye strain after some prolonged time of the computer use. There is a need to objectively assess the vision right at that time in order to either adjust the viewing conditions or determine the need for a break. Some devices (such as described in H293) allow for the instant vision testing while some others do not. But even then, once such factors as the position of the person in front of the monitor or the brightness of the screen change, the CFF reading and analysis may become distorted. There is a need therefore for a method and a device allowing for instant vision examination at the working place without changing the lighting and viewing conditions of the person and the visual settings that surround him.
In addition to the position and distance of the person from the monitor, the very viewing conditions of a particular computer monitor screen with a particular computer application displayed on that screen effect the vision function of a person in a sense that they cause eye strain to a different degree. It is important therefore to determine the CFF for the particular visual situation that the person encounters at a particular time. No testing devices of the prior art are capable of providing for such a testing ability. The need exists therefore for a method and a device allowing for objective visual testing conducted within the scope of routine viewing conditions of a person.
If it is found that the CFF readings have declined as compared either with the normal physiological range or a routine reading for this particular person, the viewing conditions of the monitor screen may be adjusted to allow for better vision and reduce the eye strain. For example, the brightness, contrast or color settings may be used to achieve that change. The need exists therefore for a method and a device allowing the person to determine the optimal viewing conditions and once adjusted to verify the positive effect of the change by determining the CFF value under these new viewing conditions.
Finally, the need exists for a device or a computer program allowing to install the vision examination program as a software application for the use with a personal computer. Such program should allow to address not only all the previous needs, but also to accumulate the vision test data for each individual user, all to be used for determining the trend and warn of a pathological condition.